Vane pump with ramp on minor diameter

ABSTRACT

A hydraulic pump of the vane type wherein the cam surface of the stator is formed with a ramp on the minor diameter portion traversed by the vanes as they move from the pressure zone to the suction zone. When vanes of the two lip type are used, an in-ramp is especially desirable for pumps wherein the vane are spring operated, while an out-ramp is especially desirable for pumps wherein the vanes are operated by hydraulic actuators. The provision of such ramps has been found to improve radial balance of the rotor, vane tip sealing, and to reduce pressure ripple, as well as wear.

United States Patent [191 Adams et a].

VANE PUMP WITH RAMP 0N MINOR DIAMETER v Inventors: Cecil E. Adams; James C. Swain; Jack W, Wilcox, all of Columbus, Ohio Assignee: Abex Corporation, New York, NY.

Filed: Apr. 24, 1972 Appl. No.: 246,774

US. Cl 418/260, 418/150, 418/268 llnt. Cl. F0lc 1/00 Field of Search 418/260, 150, 268,

References Cited UNITED STATES PATENTS [4 1 Jan.15,1974

3,652,189 3/1972 Gowie ..4I8/150 3,627,456 12/1971 Gerlach ..418/268 Primary Examiner-C. J. Husar Att0rney-James S. Hight et a1.

[57] ABSTRACT A hydraulic pump of the vane type wherein the cam surface of the stator is formed with a ramp on the minor diameter portion traversed by the vanes as they move from the pressure zone to the suction zone. When vanes of the two lip type are used, an in-ramp is especially desirable for pumps wherein the vane are spring operated, while an out-ramp is especially desirable for pumps wherein the vanes are operated by hydraulic actuators. The provision of such ramps has been found to improve radial balance of the rotor, vane tip sealing, and to reduce pressure ripple, as well as wear.

15 Claims, 7 Drawing Figures PRESSURE ZONE TRANSFER ZONE SUCTION ZONE PATENTEU 3,785,758

SHEET 1 0F 2 TRANSFER ZONE PATENIE JMISIQM 3,785,758

SHEET a DP 2 MINOR I DIAMETER MINOR MINOR DIAMETER E ER RADIAL WIDTH OF KPUMPlNG SPACE 2 MINOR DIA.

'ANGULAR POSITION ON CAM SURFACE RADIAL WIDTH OF PUMPING SPACE ANGULAR POSITION ON CAM SURFACE VANE PUMP WITH RAMP ON MINOR DIAMETER This invention relates to improvements in hydraulic pumps of the type having rotor and stator members, one of which mounts vanes that engage a cam surface carried by the other member. More particularly, the invention is directed to improvements in the shape or contour of the cam surface in a pump having vanes of either the single or twolip type.

In the most common type of commercial vane pump, the vanes are mounted by the rotor for inward and outward movement in vane slots relative to the axis of rotor rotation. The tips of the vanes slide over or .track on the cam surface of the stator that encircles the rotor. The cam surface is contoured so that the spacing between it and the rotor periphery. varies around the rotor. This so-called pumping space, bounded by the rotor surface and the cam surface, is generally regarded as comprising four zones: the pressure zone, the suction zone, a transfer zone (which lies between the suction zone and the pressure zone in the direction of rotation), and a sealing zone (which lies between the pressure zone and the suction zone in the direction of rotation). The variations in cam surfacerotor spacing in these zones causes vane movement and consequent changes in the volume of the intervane spaces or transfer pockets between each pair of vanes.

The pump operates by receiving fluid through the suction port into each pocket as it traverses the suction zone, transferring the fluid in the pocket by moving it from the suction zone across a transfer zone to the pressure zone,-and expelling the fluid from the pocket to a pressure port opening tothe pressure zone by reducing the pockets volume. Thus the pocket increases in volume as it traverses the suction zone, and decreases in volume in the pressure zone. The volume decrease at the pressure zone occurs because the cam surface approaches the rotor surface more closely there. The cam surface pushes the vanes back into their rotor slots, and the projection of the vanes from the rotor is thereby diminished. The corresponding reduction of pocket volume results in the positive displacement of the fluid therein to the outlet port. The approach of the cam surface toward the rotor surface across the pressure zone is'called the pressure ramp, the term ramp being used to designate an inclined surface or approach, as opposed to an arc of fixed or constant diameter about the rotor axis. I

The volume of the intervane space is increased at the suction zone, as the cam surface recedes from the rotor surface. This outward cam surface inclination across the suction zone is referred to as the suction ramp; it is an outward ramp, as opposed to the pressure ramp which is an inward ramp- Such suction and pressure ramps are present in virtually all vane pumps and they are essential to establish the pumping action.

est diameter of any part of the cam surface, and for this reason it has commonly been referred to as the major diameteLi It is the primary function of the transfer zone to seal or isolate the pressure zone from the suction zone,

while fluid is being transferred from the one to the other. A substantial decrease in the volume of a sealed pocket in the transfer zone would result in compression of the liquid. Recently, however, in Adams et al. US. Pat. No. 3,48 l,276,"issued Dec 2, 1969, (of which two of the present applicants are co-patentees), it has been taught to establish a higher-than-outlet pressure in the transfer zone by reducing the volume of the pocket in that zone and directing an outflow of fluid through a restrictor to create a backpressure. The volume reduction is accomplished by providing a slight ramp or inward lead on the major diameter part of the cam surface, in the direction of rotation. The backpressure is applied to increase the outward force on the vanes to insure that they are held in contact with the cam surface.

Between the end of the pressure ramp and the start of the suction ramp, in the so-called sealing zone, the

vanes.

Insofar as we are aware, a ramp has not heretofore ever been provided on the minor diameter portion of the cam surface. Because of the small volume of the intervane pocket in the sealing section, a severe ramp would cause a relatively large percentage change in pocket volume, and this could lead to undesirable momentary pressurizing or cavitation of fluid therein, during the time in the cycle when two vanes are sealing on the minor diameter.

This invention is predicated on the discovery that it is advantageous to provide a ramp, of certain small angulation, on the minor diameter of the cam surface. Such a ramp provides the grestest advantages in a certain sub-class of vane pumps, viz., those which have vanesof the two-lip type, but it is also useful with vanes of the single lip type.

Vanes of the two-lip type are known per se, and are shown for example in the above mentioned Adams et al patent. Such vanes are characterized by two circumferentially spaced cam surface engaging edges or lips, between their front and back faces. These lips comprise a leading lip and a trailing lip, and they are separated by a groove between them. The groove providesfluid communication and pressure balance between the top and bottom of the vane. Both lips of the vane are intended to engage the cam surface where the surface is We have found, however, that that is not the most dc sirable configuration. It is probably impossible, or at least very impractical in the commercial production of pumps, to produce a cam ring having a sealing zone surface that is truly concentric with the center of rotor rotation. ln fact, if viewed under great enlargement, a

standard commercially produced cam surface can be considered as comprising a wavy line, or as having tiny deviations from the theoretical true radius shape. Even a surface that approximates a precision constant diameter will seldom, if ever, by perfectly concentric with the shaft centerline in the final pump assembly. This is because all individual parts require dimensional tolerance for manufacturing, as well as tolerances for concentricity of various diameters on circular components. This can allow looseness or shifting of the cam relative to the housing and shaft. Even though the unassembled cam ring may have a minor cam surface closely concentric with the outside diameter, after it has been assembled into the pump the outside diameter is unlikely to be perfectly concentric with the center of rotation of the shaft and rotor, due to the manufacturing tolerances described.

Therefore, the minor cam surfaces may be eccentric with the center of rotation in a somewhat random mount and direction from pump to pump. This eccentricity may introduce the need for a vane, if it is to track the cam, to move into or out of a vane slot as the vane traverses a minor sea] surface, or even require the vane to undergo both directions of movement in sequence on the same sweep across this seal surface. This same eccentricity in the installed'cam may require that a vane directly opposite the first vane move out as the first vane moves into the slot, or in, as the first vane moves out. This produces a somewhat random and unpredictable need for slight vane stroking or radial movement during the vane sweep across the minor seal, with no assurance that vanes 180 apart are undergoing the same direction or magnitude of stroking.

The problem is further aggravated by the fact that the cam will have one shape or contour as manufactured, but will distort slightly into a different shape when in a pump that is running under pressure. The magnitude of the distortion increases with higher pressure. This distortion is made worse by the fact that some of the inter nal cam surfaces are under the influence of outlet pressure, with other surfaces exposed to the lower inlet pressure, with some surface areas cycling between inlet and outlet pressures as vanes reach and leave the ports. This results in a cyclic distortion of the cam relative to the manufactured shape.

Although in the industry it has been accepted and standard practice to provide a minor cam surface which is intended to be concentric with the center of rotation, with no apparent need for vane stroking during the sweep across this minor seal surface, we have discovered that this design produces certain undesirable results. The undesirable results stern from the random deviations from the theoretically perfect concentric arcs on the minor cam surfaes, resulting from commercial quality cam manufacturing, eccentric assemblies, and cam distortion, as described.

We have found that such imperfect minor cam surface shapes lead to effects that are detrimental in several respects. At a point where the cam surface is leading inwardly, when two-lip vanes are used, then the front lip of the two-lip vane will bear on it; but at an adjacent point where the cam surface is leading outwardly, then the rear lip of the vane will bear on it. Thus, as a two-lip vane moves across an imperfect or rippled" minor diameter, the line of contact of the vane with the surface may shift repeatedly between the leading lip and the trailing lip. This shifting of the line of contact from lip to lip may occur very rapidly, many times a second in a vane pump that rotates at L800 to 2,400 rpm. It is a source of noise and tip wear.

in addition, shifting of the line of vane-cam surface contact is a significant cause of irregular hydrostatic unbalance of the rotor, causing erratic and heavy shaft bearing loads. This can be seen from the following analysis: when the vane is moving across the sealing zone, pressure at the pressure zone acts on the rear face of the vane, while the front of the vane is exposed to the low pressure of the suction zone. When the front lip of the vane engages the cam surface minor diameter and the trailing edge of the vane is not forming a seal, the vane groove and most of the top of the vane is exposed to and sees the pressure from the pressure zone. The pressure is reflected trhrough the radial passage in the vane to the vane bottom, and also to the vane slot in the rotor. However, when the trailing lip of the vane is engaging the cam surface, the top and bottom of the vane and the rotor slot will see the low pressure at the suction zone. Thus, the rotor slot is alternately pressurized and depressurized by the in-out variations of the cam surface. At times when a rotor slot, with its vane traversing one minor seal surface, is thus exposed to pressure, and, due to this erratic operation, the vane slot away from it is exposed to suction pressure, the rotor will develop a side load in one direction. If the high and low pressures in the slots are reversed, the side load will reverse directions. This will establish a substantial but fluctuating radial load on the rotor shaft. The load, in this case, will be the product of the pressure difference in the two slots times the cross-sectional area of a vane. In a pump operationg, say, at 3,000 psi and having a vane cross-sectional area of one-half square inch, the radial force on the rotor can be as much as three-fourths of a ton, and may be applied and released many times a second. The sudden application and release of a force of this magnitude is believed to set up pump vibration, noise, shaft deflection, and to increase wear, and may break the seal between the vane and cam, producing erratic cross-port leakage with associated problems.

We have found that the provision of a ramp-either an in ramp or an out-rampon the cam ring minor diameter will obviate this problem if the ramp has an inclination just sufficient to insure that the lip-the same lipof the vane always remains in contact with the cam surface. Such a ramp insures that, regardless of minor imperfections on the ramp itself, one lip of a two-lip vane will always be closer to the minor diameter cam surface than the other, and the other lip can never engage the ramp. If the ramp is an in ramp, then the leading lip will track on it and the trailing lip will at all times (in the sealing zone) be spaced from the ramp. On the other hand, if the ramp is an out-ramp, then the trailing lip will engage it and the leading lip will not. Load shifting on the rotor is thereby prevented.

There is in addition a second and more subtle aspect of the invention. This concerns the relative desirability of an in-ramp as compared to an out-ramp in the sealing zone. We have found that while a ramp of either type is better than no ramp at all, an in-ramp is more desirable than an out-ramp in certain circumstances, and less desirable in others. There is an advantage to one type over the other, depending on the means by which the vanes are biased toward the cam surface.

Two general types of vane actuating means are well known in the art: springs and hydraulic actuators (for example, pistons). One or more springs can be mounted in the rotor beneath each vane to bias it toward the cam surface. Alternatively, as shown in Adams and Sun U.S. Pat. No. 2,832,293, a piston can be mounted in the rotor beneath the vane and operated by pressure fluid from the pressure zone to apply a pressure dependant force to hold the vane against the 5 cam surface.

The reason for this peculiar relation follows: the pressure behind the vane on an in-ramp will act across the top of the (non-engaging) trailing lip of a two-lip vane and through the vane groove to the bottom of the vane, and will act over the entire bottom area of the vane to urge it outwardly. That same pressure does not, however, actover the entire cop of the vane, because the small area which is in front of the line of contact between the leading lip of the vane and the cam surface is exposed to suction zone pressure. Therefore a small net outward pressure force exists, which adds to the spring force to urge the vane outwardly. On the other hand, it can be seen by a similar analysis that if the ramp were an out-ramp, only the trailing lip would engage the cam surface, and that a net presusre in-force would act upon the part of the vane which is exposed to pressure which would decrease the total outward force of the vane. For this reason, it is preferable that, for vane pumps having spring operated two-lip vanes, the minor diameter of the cam surface should have an in-ramp. v g g A A different situation obtains for hydraulic-actuated vanes in which an inward facing surface of each vane is exposed to high pressure. Full details of one such construction are given in Adams et al. U.S. Pat. No. 3,223,044, issued Dec. l4, 1965 and titled Three Area Vane Type Fluid Pressure Energy Translating Device." As shown in that patent, the pressure force on each piston-type hydraulic actuator urges the respective vane outwardly. The top and bottom of the vane are connected by the vane groove described above, and when the leading lip of the vane is contacting the cam surface across the sealing zone, most of the cop of the vane is exposed to pressure. This pressure is applied to,

and reflected on the bottom of the vane. Since nearly or essentially the same pressure is applied to both the top and the bottom of the piston, the entire force of the piston is almost balanced out and cancelled. Hence, no or only a very small force acts on the vane from the piston to hold it outwardly, leaving very little vane bias except centr ifug al force resulting from rotor rotation.

Use of an out-ramp in the sealing zone for piston operated vanes insures their effectiveness, by insuring that the piston force will not-be balanced out or. cancelled in the manner just described for an in-ramp. With an out-ramp, the trailing lip of the vane will engage the cam surface, and the top of the vane (all except for the area in back of the line of contact of the rear lip with the cam surface) will be exposed to the low pressure of the suction zone. This low pressure is applied to the bottom of the. vane and is insufficient to offset the force of the piston. Thus, the piston will always be effective to produce the sealing force for which it is provided.

In either case, the amount of the ramp should not be substantially more than that angulation which is needed just to insure that the same lip of the vane will remain in contact with the cam surface across the sealing zone, considering the unavoidable irregularities in the inclination of the ramp. This angulation may be essentially constant along the length of the sealing zone, and generally will be in the range of about W to 1% or 2, for either an in-ramp or an out-ramp. Ramps less than would not be sufficient'to overcome the problems of eccentric assemblies and distortion of the cam from pressure that could cause lip switch; on the other. hand, ramp angulations greater than about 2 tend to cause trapped volume changes which are relatively so great as to result in excessive pressure increase in the sealing zone from fluid compression, or in cavitation, during the moment when two vanes are sealing on the minor diameter, between ports.

Another undesirable result of the earlier described random deviations from a truly concentric minor seal surface is common to the use of both single and two-lip vanes. Both types of vanes require either springs or hydraulically actuated means for urging them towards the cam surface to maintain the sealing contact. For each individual vane design, a level of force from the actuators must be provided to overcome vane to rotor slot friction, if the minor cam surface deviations at any time require outward vane movement to maintain the seal. During this outward movement of the vane, the friction force subtracts from the actuator force, to leave a relatively low net outward force. At a different position on the minor cam surface, where the deviation in the surface contour causes the vane to be moved inwardly in the rotor slot, the frictional force adds to the force of the actuator. This variable force level results in substantial and sudden variations in contact force between the vane tip and cam, which encourages-vane tip wear and uneven wear on the cam surface. This uneven wear on the cam surface is believed to be highly undesirable and will usually shorten the life of the pump.

To avoid this undesirable reversal of vane movement and the erratic vane to cam loading that results from it, the same magnitude of ramp angle on the minor diameter as described is useful on single lip vanes as well as on double lip vanes. Either an inward or outward sloping ramp will prevent the reversal of vane movement and thus this improvement is automatically obtained with two-lip vanesif the selection of the direction has been to satisfy the conditions previously described.

When single lipvanes are used, either direction of .ramp will also prevent the reversal of the friction force.

The actual selection of the direction would depend on the details of the vane actuator design, and whether it is desired to increase the vane to cam loading by inward movement so that the friction force adds to the actuator force, or outward movement so that the friction reduces the net vane to cam loading. In either case, the vane to cam bearing loads will be more uniform across the full span of the minor seal surface, than if the minor diameter were manufactured in accordance with past practice.

The invention can best be further described by detailed reference to the accompanying drawings in which:

FIG. 1 is an end plan view of the rotor and stator assembly of a balanced reversible pump with piston operated twolip vanes, in accordance with a preferred embodiment of the invention;

FIG. 2 is an end plan view of the stator of FIG. I, superimposed on a polar graph, and shows in exaggerated form the several operating segments of the cam surface which constitute the minor and major diameters and the pressure and suction ramps;

FIG. 3 is an enlarged fragmentary view of a piston opeated vane in contact with an out-ramp on the cam surface in the sealing section of the pump, the ramp inclination being greatly exaggerated;

FIG. 4 is a view similar to FIG. 3, but shows the altered pressure relationsthat would exist if the vane rode on an in-ramp instead of an out-ramp in the sealing section;

Hg. 5 is a view similar to FIG. 4 but shows a spring operated vane in contact with an in-ramp on the cam surface in the sealing zone, the ramp inclination again being greatly exaggerated;

FIG. 6 is a graph which shows the radial width of the pumping zone, i.e., the vane displacement, as a function of angular position on a cam surface with an outramp on the minor diameter; and

FIG. 7 is a graph similar to FIG. 6, but shows the radial displacement of the vane as a function of position along the cam surface for a pump having an inward ramp on the minor diameter, also in accordance with the invention. 7

The following detailed description uses as an example a balanced reversible vane pump wherein the cam ring is symmetrical about a line through its center and has pairs of pressure, sealing, transfer and suction zones diametrically opposite to one another. Such a cam ring is reversible to provide alternate directions of rotation. However, it should be understood that the invention is not limited to use in balanced reversible pumps, and may be used in unbalanced and nonreversible pumps as well. Reversible cam rings per se are old in the art, and reference may be had to U.S. Pat. No. 3,223,044 for a complete explanation of the reversal mechanism. 7

A pump rotor is designated at l in the drawings. The rotor is driven by a shaft 2, and mounts a plurality of vanes, each designated at 3, that reside in individual vane slots 4 in the rotor. The vanes are of the two-lip type, and at their outer edges engage a cam surface 5 which is presented on a cam ring or stator 6. Stator 6 and rotor l comprise an operating assembly in a pump body, not shown.

Those skilled in the art will be familiar with the conventional pump environment in which the rotor and cam ring are disposed, and for that reason the background details of the pump in which the rotor and cam rings are embodied are not set forth herein. For purposes of reference the rotor and cam ring may be incorporated in a pump of the general type shown in U.S. Pat. No. 3,223,044 previously referred to.

The cam surface 5 is contoured so that pairs of diametrically opposite low presusre, inlet or suction zones at 10, transfer zones at ll, high pressure outlet or exhaust zones at 12, and sealing zones at 13,, are defined in the pumping space 14 between the cam surface 5 and the rotor l, as designated inFIG. 1. In order to provide these zones, cam surface 5 is formed in part from a pair of opposed arcs which extend across the transfer zones 11. While these arcs 15 are frequently called the major diameter part of the cam surface (see FIG. 2), they may have a slight ramp or inward lead in the direction of rotation. (In the drawings the direction of rotor rotation is shown as being counterclockwise). A second pair of arcs 16 of shorter radius than the major diameter arcs 15 extend across the respective sealing zones 13 and define what is called the minor diameter portion of the cam surface. The pairs of arcs l5 and 16 are interconnected by suction ramps I8 and pressure ramps 19, which extend across and bound the suction zone [0 and pressure zone 12. Together the rotor and vanes constitute a rotatable cartridge within the stator. The side edges of the vanes slide over surfaces of front and back cheek plates (not shown) on opposite sides of the rotor, which may be conventional.

The pairs of adjacent vanes divide the pumping space between the rotor, the cam surface, and the cheek plates into a series of transfer pockets. Individual pockets are designated at 25 in FIG. 1. As it rotates, each pocket rceives fluid at the suction ports 20, which open to the respective suction zones 10, and delivers it to the pressure ports 22 which communicate with the respective pressure zones 12.

In accordance with the invention, the so-called minor diameter part 16 of the cam surface, instead of being a true arm or constant radius about the rotor center 17, has a slight ramp or lead. The distance from the center 17 of rotor rotation to cam surface 5 progressively changes along this minor diameter arc. For clarity, the extent of this ramp is greatly exaggerated in the drawings, the ramp being much less than appears.

The ramp shown in FIGS. 1 and 2 on the sealing zone or minor diameter part of the cam ring is an out-ramp. By reference to the concentric circles shown in FIG. 2, it will be seen that, with reference to the assumed counterclockwise direction of rotor rotation, the ramp progressively recedes from the center 17.

Use of such an out-ramp is desirable where the vanes are operated by hydraulic pressure operated means such as pistons. One form of such hydraulic pressure operated means is shown in FIGS. 1 and 3. One or more pistons, each designated at 27, are supported for radial sliding movement in bores in rotor I. These bores extend inwardly toward the center of the rotor from the inner ends 26 of the vane slots. At the inner ends the piston bores are all connected by a circumferential channel in the rotor around shaft 2. This channel, not shown in the drawings, is supplied with pressure fluid from the pressure zone of the pump in a manner known per se, as for example shown in U.S. Pat. Nos. 2,832,293 and 3,223,044. The inner end of each piston is exposed to high pressure, but the outer end of the piston and the bottom of the vane in the slot end 26 are exposed to the pressure that prevails in slot 26 which varies as the rotor rotates.

FIG. 3 shows, at a greatly exaggerated angle, the contact between a hydraulic piston operated vane 3a and the minor diameter'part 16 of the cam surface in the sealing zone. The front lip of this vane 3a is designated at 29, and the trailing or rear lip is designated at 30. Since the minor diameter l6 has an out-ramp, the trailing vane lip 30 is in contact with the ramp, and front lip 29 is spaced slightly below the cam surface. The trailing face or surface 31 of the vane is exposed to pressure P from the pressure zone (see FIG. 1). The

leading face or surface 32 of vane 3a is exposed to suction designated by the letter S, since that face of the vane is in communication with the suction zone 10. The suction zone pressure acts on leading lip 29 of vane 3a and in the groove 33 that is between the two lips of the vane. Groove 33 applies the (low) suction zone pressure to the bottom surface 34 of vane 3a in the bottom 26 of the rotor slot. Thus, a low pressure acts over the entire inner end 34 of the 'vane, and across most-but not all-of the top of the vane.

Both the leading lip and the trailing lip of the vane have a slight round, as designated at 3%. These rounds are formed on the lips adjacent the front and rear faces 29 and 30 of the vanes. It will be noted that there is a small area designated at 36, behind (i.e., to the right in FIG. 3) of theline of contact 37 of the vane trailing lip 30 with the minor diameter 16. The tip area 36 sees or is exposed to the pressure P from the pressure zone. Apart from this small area on the top of the vane-perhaps 2 percent of the total area of the top the vane-the top and bottom of the vane are at essentially the same low pressure, and hence are pressure balanced, so that there is no net pressure force on them. The force applied to the hydraulic piston pin 27 is effectiye to urge the vane outwardly.

As previously explained, if the leading lip of the vane were tracking on an in-ramp (shown for purposes of comparison in FIG. 4), the force of the piston would largely be balanced by equal and opposite high pressure forces in slot 26 and the piston would contribute l tls issiaastfsa.

In substance, it can therefore be said that the provision of an out-ramp on the minor diameter 16 insures the effectiveness of hydraulic piston vane operating means, and prevents neutralization of the piston force.

FIG. 6 of the drawings is a graph which illustrates or develops the radial distance between the cam surface and the rotor surface 23, as a function of angular po-' sition around the cam, starting (arbitrarily) from the beginning of the suction ramp. The graph includes. slightly more than 180 of cam surface length, and for theb alanced cam ring'siiawmrwm be understood that the entire cam surface will include two full cycles, only one of which is shown.

As shown in FIGS. I and 6, in the direction of rotor movement, indicated by the arrows, the suction ramp 18 (designated in FIG. 6 as the portion 40 of the curve) progressively recedes from the periphery 23 of the rotor 1 across each suction zone 10, so that the volume be in the approximate range of W to 2. This is about the minimum amount necessary to insure that lip switching will not occur.

Where the pump is to be used with spring operated varies, the ramp should be an in-ramp. This is illustrated in FIGS. 5 and 7. In FIG. 5, a spring actuated vane is shown in contact with an in-ramped minor diameter 16 of the cam ring. The vane is urged outwardly by one or more springs designated at 48 which at its end is received in sockets in the rotor and vane. In this case the leading lip 49 of the vane is in contact withthe ramp on minor diameter 16, and the trailing lip 50 is spaced from the cam surface. Thus the vane groove 51 communicates the pressure P behind the vane to the bottom 52 of the vane. The small area 53 adjacent the leading face of the vane and in front of the line of contact 54 between the leading lip 49 and cam surface 5 is exposed to suction S. The force on this area is overbalanced by a pressure force on the corresponding area at the bottom 52 of the vane, and the resulting net pressure force assists the force of spring 48 in holding the vane outwardly. Thus, use of an in-ramp on the cam ring for spring operated vanes provides an additional pressure assist for thespring. Moreover, the in-ramp establishes positive contact of the vane with the cam of a transport pocket 25 between a pair of vanes is increased in that zone. Across the transfer zone ill the major diameter part 15 of the cam surface 5 very slightly approaches the rotor (as designated at M in FIG. 6) as known in the prior art. Across the pressure zone 12 the pressure ramp 19 more steeply approaches the rotor (curve portion 42) as it comes into close proximity with the rotor periphery, in the sealing zone 13. Thus, as the vane moves onto the pressure ramp, it

moves iwnardly and reduces the intervane pocket area, a

and thereby displaced to the pressure port 22.

. v6 movement of the cam surface away from the rotor. The

ramp angulation is designated at 44, and preferably is about /2", but as previously stated can advantageously surface, whereas if an out-ramp were used, the force of the spring might or might not be sufficient to accelerate the vane, as well as overcome the substantial vane to slot friction, sufficiently to maintain tracking.

A development of the cam surface shape for a spring operated vane is shown inFIG. 7. In comparison to FIG. 6, it will be noted that here the minor diameter leads inwardly in the direction of rotation, rather than outwardly. Again the angulation of the inward ramp 55 can be constant, and in the range of 3 4 to about 2. In a typical pump, this may amount to about 0.010 inches of inward vane travel in 1.25 inches of cam surface length.

The foregoing detailed description refers directly to the illustrated construction with two-lip vanes. Hoewever, from what has been said previously herein concerning single lip vane pumps, those skilled in the art will understand the utility and application of a minor ramp in pumps of the latter type as well.

Having described the invention, what is claimed is:

I. In a vane type hydraulic pump having rotor and stator members and vanes mounted in vane slots in one memberfor engaging a cam surface presented by the and the suction zone, said vanes being provided with means for biasing them towards the cam surface,

the improvement comprising,

a ramp on said cam surface extending substantially across said sealing zone, said ramp being an outramp and having an angulation of about 5 1 2 and allowing the vanes to move only radially outward relative to the center of rotation of the rotor, as said vanes traverse said sealing zone in sealing engagement with said ca m surface.

2. The improvement of claim I wherein said vanes are of the two-lip type.

3. The improvement of claim 1 wherein said vanes are of the two-lip type and are urged toward the cam surface by hydraulic pressure operated means acting thereon.

4. The improvement of claim 1 wherein said vanes are of the single lip type.

5. The improvement of claim 1 wherein the angulation of the ramp is selected to assure a continuous movement of the vanes in one direction relative to the center of rotation of the rotor, thereby avoiding changes of vane-to-rotor slot friction force which changes would affect the magnitude of the bearing force of the vane tip on the cam surface.

6. The improvement of claim 1 wherein the angulation of the ramp is adequate to provide the said radial vane motion in a pump having a slightly eccentric assembly of its individual components and which pump in operation displays distortion of the cam surface as a result of internal operating pressure.

7. The improvement of claim 1 wherein the vanes are of the two-lip type and the ramp angulation is substantially the minimum angulation which maintains contact of the cam surface with the same lip of the vane as it traverses said sealing zone.

8. In a vane pump having vanes of the two-lip type which engage a cam surface, said cam surface including a minor diameter portion, the improvement comprising,

a ramp on the said minor diameter portion of the cam surface,

said ramp being at substantially the minimum angulation necessary to insure that a selected lip of each vane will continuously contact the cam surface across the said minor diameter portion.

9. A method of preventing lip switching as a two-lip vane moves across the minor diameter portion of the cam surface of a vane pump, said method comprising,

angulating said minor diameter portion at an angle in the approximate range of 2 with respect to a circumferential line through the lip of the vane which is in contact with said minor diameter portion.

10. The method of claim 9 wherein said angulation is substantially the minimum angulation necessary for the same lip of each vane to contact the said minor diameter portion regardless of waviness or irregularities in the curvature of said minor diameter portion.

ll. in a vane pump having vanes of the two-lip type and wherein the tops and bottoms of the respective vanes are hydraulically interconnected and the lips of the vanes engage a cam surface having a minor diameter surface portion, the improvement comprising,

a ramp on the said minor diameter portion of the cam surface,

said ramp being at an angulation and direction such as to maintain a first lip only of each said vane continuously in contact with said minor diameter portion while the respective vane is traversing it, the second lip of the said vane being spaced from the cam surface, the source of pressure exposed to the vane top and vane bottom thereby being unchanging as the vane traverses the minor diameter portion.

12. The improvement of claim 11 wherein the source of pressure to which the said vane top and vane bottom are exposed, is that intervane pocket which is adjacent to and in communication with the said second lip of the said vane.

13. In a vane type hydraulic pump having rotor and stator members and vanes mounted in vane slots in one member for engaging a cam surface presented by the other member, a pressure zone and a suction zone in the pumping space between the one member and said cam surface, a transfer zone and a sealing zone in said pumping space alternately between the pressure zone and the suction zone, said vanes being provided with means for biasing them towards the cam surface,

said vanes being of the two-lip type,

the improvement comprising,

a ramp on said cam surface extending substantially across said sealing zone, said ramp having an anguynpf abqu -Z" Q1h EQQi$1YEUEEFEYEFE9 said sealing zone in sealing engagement with said cam surface, they move radially in a single direction thereon relative to the center of rotation of the rotor.

14. The improvement of claim 13 wherein the vane biasing means are springs,

and wherein said ramp is an in-ramp.

15. The improvement of claim 13 wherein the vane biasing means are hydraulically actuated,

and wherein said ramp is an out-ramp. 

1. In a vane type hydraulic pump having rotor and stator members and vanes mounted in vane slots in one member for engaging a cam surface presented by the other member, a pressure zone and a suction zone in the pumping space between the one member and said cam surface, a transfer zone and a sealing zone in said pumping space alternately between the pressure zone and the suction zone, said vanes being provided with means for biasing them towards the cam surface, the improvement comprising, a ramp on said cam surface extending substantially across said sealing zone, said ramp being an out-ramp and having an angulation of about 1/4 * - 2* and allowing the vanes to move only radially outward relative to the center of rotation of the rotor, as said vanes traverse said sealiNg zone in sealing engagement with said cam surface.
 2. The improvement of claim 1 wherein said vanes are of the two-lip type.
 3. The improvement of claim 1 wherein said vanes are of the two-lip type and are urged toward the cam surface by hydraulic pressure operated means acting thereon.
 4. The improvement of claim 1 wherein said vanes are of the single lip type.
 5. The improvement of claim 1 wherein the angulation of the ramp is selected to assure a continuous movement of the vanes in one direction relative to the center of rotation of the rotor, thereby avoiding changes of vane-to-rotor slot friction force which changes would affect the magnitude of the bearing force of the vane tip on the cam surface.
 6. The improvement of claim 1 wherein the angulation of the ramp is adequate to provide the said radial vane motion in a pump having a slightly eccentric assembly of its individual components and which pump in operation displays distortion of the cam surface as a result of internal operating pressure.
 7. The improvement of claim 1 wherein the vanes are of the two-lip type and the ramp angulation is substantially the minimum angulation which maintains contact of the cam surface with the same lip of the vane as it traverses said sealing zone.
 8. In a vane pump having vanes of the two-lip type which engage a cam surface, said cam surface including a minor diameter portion, the improvement comprising, a ramp on the said minor diameter portion of the cam surface, said ramp being at substantially the minimum angulation necessary to insure that a selected lip of each vane will continuously contact the cam surface across the said minor diameter portion.
 9. A method of preventing lip switching as a two-lip vane moves across the minor diameter portion of the cam surface of a vane pump, said method comprising, angulating said minor diameter portion at an angle in the approximate range of 1/4 * - 2* with respect to a circumferential line through the lip of the vane which is in contact with said minor diameter portion.
 10. The method of claim 9 wherein said angulation is substantially the minimum angulation necessary for the same lip of each vane to contact the said minor diameter portion regardless of waviness or irregularities in the curvature of said minor diameter portion.
 11. In a vane pump having vanes of the two-lip type and wherein the tops and bottoms of the respective vanes are hydraulically interconnected and the lips of the vanes engage a cam surface having a minor diameter surface portion, the improvement comprising, a ramp on the said minor diameter portion of the cam surface, said ramp being at an angulation and direction such as to maintain a first lip only of each said vane continuously in contact with said minor diameter portion while the respective vane is traversing it, the second lip of the said vane being spaced from the cam surface, the source of pressure exposed to the vane top and vane bottom thereby being unchanging as the vane traverses the minor diameter portion.
 12. The improvement of claim 11 wherein the source of pressure to which the said vane top and vane bottom are exposed, is that intervane pocket which is adjacent to and in communication with the said second lip of the said vane.
 13. In a vane type hydraulic pump having rotor and stator members and vanes mounted in vane slots in one member for engaging a cam surface presented by the other member, a pressure zone and a suction zone in the pumping space between the one member and said cam surface, a transfer zone and a sealing zone in said pumping space alternately between the pressure zone and the suction zone, said vanes being provided with means for biasing them towards the cam surface, said vanes being of the two-lip type, the improvement comprising, a ramp on said cam surface extending substantially across said sealing zone, said ramp having an angulation of about - 2* so that as Said vanes traverse said sealing zone in sealing engagement with said cam surface, they move radially in a single direction thereon relative to the center of rotation of the rotor.
 14. The improvement of claim 13 wherein the vane biasing means are springs, and wherein said ramp is an in-ramp.
 15. The improvement of claim 13 wherein the vane biasing means are hydraulically actuated, and wherein said ramp is an out-ramp. 